Hot gas generator

ABSTRACT

A hot gas generator wherein liquid fuel is supplied to an annular heated reservoir surrounding the burner, whereby the heated fuel heats the walls of the combustion chamber, thereby enabling the generator to attain relatively high output temperatures in very short periods of time. The generator is useful in starting gas turbine engines, i.e. by discharging high temperature, high pressure gas through a nozzle into the blades of the turbine to initiate turbine rotation.

United States Patent [1 1 Croker [63] Continuation-impart of Ser. No.274,786, July 24,

I972, abandoned.

[52] U.S. C1 60/39.71; 60/3974 R; 431/173; 431/242; 43l/243 [51] Int.Cl. F23D 11/24; F23D 11/44 [58] Field of Search 60/3969, 39.71, 260,267, 60/3914, 39.48, 39.7, 39.13, 39.74 R; 431/173, 242, 243

[56] References Cited UNITED STATES PATENTS 929.077 7/1909 Calkins431/243 1,686.213 10/1923 Koudritsky 431/173 1,821,752 9/1931 Fisher431/243 2.503.702 4/1950 Beggs...... 431/243 2589215 3/1952 Atwood60/267 451 Sept. 9, 1975 2,729,060 1/1956 Allen ct a1. 60/3914 2,872,7822/1959 Johnson et al 60/3969 2.881844 5/1959 Coty 60/3971 2,922,2791/1960 Roberson et al... 60/39.71 1099,910 9/1963 Schirmer et a1...60/3974 R 3.431.743 3/1969 Green 60/3948 3,533,233 10/1970 Fiedler et31.... 60/3914 3,703.259 11/1972 Sturgess ct al. 60/3974 R 3.7395766/1973 Chamberlain 60/3974 R 3.847534 11/1974 Nomaguchi et a1... 431/2433,857,672 12/1974 Reed et a1 431/173 Primary ExaminerWilliam L. FreehAssistant ExaminerR0bert E. Garrett Attorney, Agent, or Firm-Peter A.Taucher; John E. McRae', Robert P. Gibson [57] ABSTRACT A hot gasgenerator wherein liquid fuel is supplied to an annular heated reservoirsurrounding the burner, whereby the heated fuel heats the walls of thecombustion chamber. thereby enabling the generator to attain relativelyhigh output temperatures in very short periods of time. The generator isuseful in starting gas turbine engines. i.e. by discharging hightemperature, high pressure gas through a nozzle into the blades of theturbine to initiate turbine rotation.

5 Claims, 2 Drawing Figures HOT GAS GENERATOR RELATION TO OTHER PATENTAPPLICATION This is a continuation-in-part of an earlier filed Pat.application, Ser. No. 274,786 filed on July 24, 15172, now abandoned inthe name of the present inventor, and assigned to the United StatesGovernment.

BACKGROUND OF THE INVENTION Previously it has been proposed to use hotgas generators for initiating rotation of turbine engines. For example,see US. Pat. 2,775,866 issued to K. B. Randall; US. Pat. 2,921,431issued to A. C. Sampietro; US. Pat. 2,925,713 issued to R. M. Stevens;US. Pat. 2,968,152 issued to E. K. Moore; US. Pat. 3,004,387 issued toM. P. Woodward; and US. Pat. 3,707,074 issued to M. 1. Meyer et al.

THE PRESENT INVENTION The present invention proposes a hot gas generatorespecially designed to include a small burner capable of rapidly heatinghigh pressure air or other gas to a relatively high temperature on theorder of 1500 F. The heated gas can be discharged from the burnerthrough a high pressure nozzle to impinge on the blades of a turbineengine, thereby initiating engine start-up. The burner is located toextend through an annular fuel supply reservoir that is maintained in aheated condition, e.g. at 100 F, whereby the fuel in the reservoir heatsthe burner surfaces; the aim is to enable the burner to rapidly heat thesupply air to a high temperature, even when the apparatus is located inartic atmosphere. The annular fuel reservoir is pressurized prior toburner ignition; at burner ignition the pressurized fuel is injectedinto a stream of high pressure oxidizer gas (compressed air) to form acombustible mixture. This mixture passes through a narrow annularpassage that is radially interposed between the combustion chamber andthe heated fuel reservoir. The mixture is therefore heated when itenters the combustion chamber. The chamber arrangement promotes therapid attainment of a high temperature, high pressure condition at theburner outlet without flame flashback or useless back pressure effects.

THE DRAWINGS FIG. 1 is a sectional view through one embodiment of theinvention, taken generally on line 1-1 in FIG. 2.

FIG. 2 is a sectional view taken on line 22 in FIG.

FIGS. 1 and 2 illustrate a hot gas generator comprising an annular fuelreservoir 12 having an inner wall 14 and an outer wall 16. Liquid fuelis initially supplied to reservoir 12 by means of a fuel pump 18 locatedin a line 19 containing a solenoid valve 20 and check valve 22. Theliquid fuel enters chamber 12 through a port 24.

After chamber 12 is completely filled with liquid fuel the fuel spacemay be pressurized by means of a high pressure air line 26 containing anelectrically operated valve 28. The line connects with reservoir 12through a port 30. Valve 28 is opened to pressurize the fuel only duringperiods when the burner is in operation; during non-operating periodsvalve 28 is closed.

Pressurized fuel is delivered upwardly through a vertical tube 32 to apressure-responsive control valve 34 that has a spring operating forcesufficient to keep the valve closed against the pressure developed byfuel pump 18. The pump pressure is effective to fill reservoir l2 andthe space to the right of ball valve 34 when the reservoir isdepressurized.

When reservoir 12 is filled and pressurized (by opening valve 28) fuelflows leftwardly past valve 34 through a nozzle opening 36 and into anair supply passage 38 for the burner; nozzle opening 36 forms a fuelintake connection to air supply passage 38. The supply air is initiallytaken from a high pressure source through a line 40 containing anelectricallyoperated valve 42. During nonoperating periods valve 42 isclosed. During burner-operating periods the air-fuel mixture flowsdownwardly through passage 38 into an annular passage 44 formed by aperipheral groove in a combustion cup element 46. Some of the airfuelmixture is forced through a number of ports 48 into the cup interiorspace 50 near the sparking end of spark plug igniter 52. Some of themixture flows in a spinning fashion through a narrow annular inlet space54 formed by the inner surface of reservoir wall 14 and the outersurface of combustion cup side wall 56; space 54 forms a peripheralinlet for the combustion chamber. Circumferential spin is imparted tothe incoming gaseous mixture because passage 38 has a tangentialconnection to annular passage 44 (as seen in FIG. 2).

The combustion chamber is defined in part by a spherical wall 58 leadingto a discharge nozzle wall 60. A nozzle (not shown) connects wall 60 tothe vanes of a gas turbine engine, whereby hot combustion gases aredischarged at high pressure against the turbine vanes to initiateturbine start-up in the manner described in the previously mentionedpatents.

Burner start-up is initiated by switch energization of an immersionheater 62 located in the lower portion of reservoir 12. When the liquidfuel has reached an elevated temperature, e. g. F, a thermostaticoperator 64 in the upper portion of the reservoir operates a snap switch66 to start the burner operation. Operator 64 and switch 66 can bestandard shelf items. As shown in FIG. 1 operator 64 is a tube-roddevice wherein the tube has a low coefficient of thermal expansion, andthe rod has a high coefficient of thermal expansion; switch actuationresults from differential expansion.

Switch 66 is preferably arranged to control heater 62, pump 18, sparkplug 52 and the three valves 20, 28 and 42. At the actuation temperatureof 100 F the switch deenergizes heater 62 and pump 18, closes valve 20,opens valves 28 and 42, and energizes spark plug 52. Suitable relays andtransformers may be employed to accomplish the program.

Valve 28 opens to pressurize the fuel in reservoir 12. The fuel isthereby forced past valve 34 into passage 38 where it mixes with thecombustion air flowing from the now-opened line 40. Fuel-air mixturesflowing through ports 48 are ignited by spark plug 52. The rightwardlyadvancing flame front in chamber 50 ignites the mixture flowing fromannular space 54 into the combustion zone 51. The hot combustion gasesare exhausted at high pressure through a nozzle connected to wall 60.

The combustion process may be continued until the fuel level inreservoir 12 drops below the lower end of tube 32; i.e. below imaginaryline 33. After that time the continued pressurization of reservoir 12 byair line 26 is ineffective to deliver fuel to passage 38. By that timethe turbine should be operating.

The illustrated structure is believed to be advantageous in that thepreheated fuel in reservoir 12 heats the fuel and also inner wall 14;the result is believed to be improved fuel volatilization, betterfuelair homogenity, and improved combustion, even when the apparatus islocated in sub-zero temperatures.

The spin given to the mixture in groove 44 and space 54 is believed tobe advantageous in converting flow energy to pressure energy, in afashion somewhat similar to that taking place in centrifugal fans. Space54 is relatively narrow in the radial direction; e.g. about 0.06 inch,so that pressures generated by the combustion process presumably haveminimum tendency to exert shock forces backwardly through space 54.Combustion pressures would presumably have to completely disrupt thespin imparted to the entering gases before such pressures could generatea useless backward shock force; the spin energy presumably acts topreclude such action. The narrowness of space 54 would appear to offer arestriction to flame flashback while still permitting large fuel entryinto the combustion zone.

Sperherical combustion surfaces 58 probably reflects combustionpressures to establish a high pressure condition in space 51. Surface 58also acts as a throat to accelerate the gases as they are dischargedthrough the opening at 60.

Peripheral inlet space 54 is offset slightly from space 51 by reason ofthe inwardly extending surface 61; hopefully this will partially shieldthe inlet passage from shock so that high pressures are usefullydirected through opening 60 rather than backwardly into the peripheralinlet.

1 claim:

1. A hot gas generator comprising an annular liquid fuel storagereservoir defined partly by a first imperforate inner annular wall and asecond imperforate outer annular wall; means for heating the fuel in thefuel storage reservoir to thereby preheat the inner annular wall;

the inner surface of said inner wall serving to define a combustionchamber; a hollow combustion cup extending into the combustion chamber,said cup including an end wall and a third annular side wall spacedinwardly from the first inner annular wall to cooperate therewith indefining an annular fuel-air inlet space for the combustion cupinterior; an air supply passage having a tangential connection with theannular inlet space at a point near the cup end wall; means forinjecting preheated liquid fuel from the reservoir into the air supplypassage; said fuel injecting means being connected to the air supplypassage at a point upstream from the aforementioned tangentialconnection, whereby fuel and air are mixed during movement thereofthrough the passage and annular inlet space, said tangential connectionserving to impart a circumferential spin to the fuel-air mixture as itflows through the annular inlet space; and an igniter extending throughthe end wall of the cup to ignite the fuel-air mixture therewithin.

2. The generator of claim 1: said fuel injection means comprising apressure-responsive control valve effective to admit fuel to the airsupply passage only when the reservoir is pressurized.

3. The generator of claim 2: said fuel reservoir being pressurized by agas pressure means having a pressure connection in the ceiling area ofthe reservoir; said reservoir being connected to the pressure-responsivecontrol valve through reservoir outlet opening located between theceiling and floor areas of the reservoir, whereby pressurized fuel flowis discontinued upon the delivery of a predetermined quantity of fuel.

4. The generator of claim 1: said cup side wall and the inner annularwall of the reservoir being sufiiciently close to one another as toprevent flame flashback from the combustion space.

5. The generator of claim 1: the combustion cup having portstherethrough for conveying fuel air-mixtures from the annular inletspace into the cup space immediately adjacent to the ignitor ignitionpoint.

1. A hot gas generator comprising an annular liquid fuel storagereservoir defined partly by a first imperforate inner annular wall and asecond imperforate outer annular wall; means for heating the fuel in thefuel storage reservoir to thereby preheat the inner annular wall; theinner surface of said inner wall serving to define a combustion chamber;a hollow combustion cup extending into the combustion chamber, said cupincluding an end wall and a third annular side wall spaced inwardly fromthe first inner annular wall to cooperate therewith in defining anannular fuel-air inlet space for the combustion cup interior; an airsupply passage having a tangential connection with the annular inletspace at a point near the cup end wall; means for injecting preheatedliquid fuel from the reservoir into the air supply passage; said fuelinjecting means being connected to the air supply passage at a pointupstream from the aforementioned tangential connection, whereby fuel andair are mixed during movement thereof through the passage and annularinlet space, said tangential connection serving to impart acircumferential spin to the fuel-air mixture as it flows through theannular inlet space; and an igniter extending through the end wall ofthe cup to ignite the fuel-air mixture therewithin.
 2. The generator ofclaim 1: said fuel injection means comprising a pressure-responsivecontrol valve effective to admit fuel to the air supply passage onlywhen the reservoir is pressurized.
 3. The generator of claim 2: saidfuel reservoir being pressurized by a gas pressure means having apressure connection in the ceiling area of the reservoir; said reservoirbeing connected to the pressure-responsive control valve throughreservoir outlet opening located between the ceiling and floor areas ofthe reservoir, whereby pressurized fuel flow is discontinued upon thedelivery of a predetermined quantity of fuel.
 4. The generator of claim1: said cup side wall and the inner annular wall of the reservoir beingsufficiently close to one another as to prevent flame flashback from thecombustion space.
 5. The generator of claim 1: the combustion cup havingports therethrough for conveying fuel air-mixtures from the annularinlet space into the cup space immediately adjacent to the ignitorignition point.